The present invention relates to a self extinguishing type gas circuit breaker.
A known circuit breaker of this type is illustrated in FIGS. 1 to 3 of the drawings and includes a stationary terminal plate 1 on a power supply side and a load side terminal plate 10. A body member 2 has a first end fixed to the power supply side terminal plate 1, and at the opposite end of body member 2 is a nozzle 3 formed of insulating material and a stationary piston 4 formed of insulating material. A stationary arc contact 5 is fixed to terminal plate 1. A movable arc contact 6 is coupled to a driving mechanism (not shown) and is positioned to be movable thereby to be freely inserted into or withdrawn from stationary arc contact 5. A movable main contact 7 is made of an electrically conductive material and is fixed to movable arc contact 6. A power supply side stationary main contact 8 is fixed at one end thereof to the power supply side terminal plate 1 and is adapted at the other end thereof to be in sliding contact with movable main contact 7, such that current may be conducted therebetween. A load side stationary main contact 9 has one end thereof fixed to load side terminal plate 10 and the other end thereof in contact with movable main contact 7. Within the load side terminal plate 10 is a bearing 12 which supports a rod 11 which is fixed to movable arc contact 6 and which connects movable arc contact 6 and movable main contact 7 with each other. Within the interior of body member 2 is a gas storage chamber 13 containing an arc extinguishing fluid such as SF.sub.6 gas. A suction chamber 14 is defined by elements 7, 4 and 3. Nozzle 3 has a conical guide opening 15, through which communication between chambers 13 and 14 is achieved when contacts 6 and 7 have been moved to a position such that contact 6 is separated from contact 5. When contacts 6 and 7 have been fully opened to an arc extinguishing position, a gas passage 16 is formed to communicate the interior of suction chamber 14 with an exterior container (not shown) filled with the arc extinguishing fluid, i.e. SF.sub.6 gas or the like (see FIG. 3). Such exterior container for example might be a container surrounding the apparatus shown in FIGS. 1-3 and being filled with the arc extinguishing fluid. Communication between storage chamber 13 and such exterior container is achieved by a slot 17 formed in terminal plate 1. Similarly, holes 19 in terminal plate 10 provide communication of such exterior container with a chamber 18 defined by elements 7, 9 and 10. Upon use of the apparatus shown in FIGS. 1-3, an arc 20 is formed in an arcing chamber 21. The power supply side stationary main contact 8 and the load side stationary main contact 9 are coaxial and generally are concentric with terminal plates 1 and 10 and body member 2. The rod 11 which connects movable arc contact 6 and movable main contact 7 is in the form of a shaft which is coupled to the driving mechanism (not shown) and is journaled in bearing 12.
The operation of this known circuit breaker now will be described. FIG. 1 illustrates the circuit breaker in a circuit breaker closed position. Current might flow from the power supply side terminal plate 1 through the power supply side stationary main contact 8, the movable main contact 7 and the load side stationary main contact 9 to the load side terminal plate 10. A part of the current is shunted along a path which extends from the power supply side terminal plate 1 through the stationary arc contact 5, the movable arc contact 6, the movable main contact 7, and the load side stationary main contact 9 to the load side terminal plate 10.
When an arc is to be formed, a release command is given to the driving mechanism (not shown), and the movable arc contact 6 and movable main contact 7 begin to move in the direction of arrow a as indicated in FIG. 2, and such movement is by a predetermined wiping stroke. By this movement, the movable main contact 7 first is separated from the stationary main contact 8, such that all of the current then flows through element 1, 5, 6, 7, 9 and 10. Subsequently, the movable arc contact 6 is separated from the stationary arc contact 5 after a predetermined period of time, and the electric arc 20 is formed between contacts 5 and 6 in arcing chamber 21 (see FIG. 2). At this time, the movable cylindrical main contact 7 moves leftwardly as viewed in FIG. 2 in sliding contact with stationary piston 4 formed of insulating material. This contact separating motion thus increases the volume of suction chamber 14 and lowers the fluid pressure therein. The formation of arc 20 releases thermal energy which increases the temperature and pressure of the arc extinguishing fluid in arcing chamber 21, and this increased temperature and pressure fluid flows backward into gas storage chamber 13, as indicated by arrows b and b' (this phenomenon is referred to as "arc back"), and such increased temperature and pressure fluid mixes with the arc extinguishing fluid at a low temperature contained in gas storage chamber 13. Thus, the pressure of the arc extinguishing fluid in gas storage chamber 13 increases, so that movable arc contact 6 moves still further. In this case, as illustrated in FIG. 3, when the movable arc contact 6 has passed through the guide opening 15 in the forward end part of the insulating nozzle 3, the gas storage chamber 13 and the suction chamber 14 will be in communication with each other through the opening 15 and arcing chamber 21. At such time, the arc extinguishing fluid in the gas storage chamber 13 is blown out against the arc 20, as indicated by arrows c and c', and flows into suction chamber 14 through the arcing chamber 21 and the opening 15. As indicated by arrows d.sub.1 and d.sub.1 ' part of the arc extinguishing fluid is discharged into the exterior fluid container (not shown) via slot 17 provided in power supply side terminal plate 1. As the arc extinguishing fluid from the gas storage chamber 13 flows into the suction chamber 14, such fluid cools the arc 20 in the opening 15, such that the arc is extinguished and the current between contacts 5 and 6 is interrupted. Since, when the circuit breaker is in the condition illustrated in FIG. 3, the pressure of suction chamber 14 has increased, the arc extinguishing fluid in suction chamber 14 is discharged through passage 16 into the exterior container, as indicated by arrows e and e'. Thus, the condition of insulation between the stationary arc contact 5 and the movable arc contact 6 is maintained, and interruption of the arc is completed.
The above description is of the operation of the circuit breaker of FIGS. 1-3 under high current conditions. There now will be described the manner of interruption of the arc under conditions where the current flowing between the terminal plates 1 and 10 is of low or medium value. As illustrated in FIG. 3, when the movement of the movable main contact 7 has increased the volume of the suction chamber 14 and lowered the fluid pressure therein, the fluid of low temperature and high insulating property flows from the exterior fluid container via slot 17 into suction chamber 14 while crossing the arc 20, as indicated by the dotted arrow lines d.sub.2 and d.sub.2 '. This is due to the fact that the thermal energy generated by the arc is not sufficient to increase the pressure in chamber 13 to a level required to cause passage of fluid from chamber 13 through slot 17, as indicated by arrows d.sub.1 and d.sub.1 '. When the arc extinguishing fluid crosses the arc 20 in opening 15, the arc 20 is cooled and the thermal energy thereof is absorbed, such that the current is interrupted at a zero current point. The pressure of the suction chamber 14 rises due to the absorption of the thermal energy of the arc 20, whereby the fluid is discharged through passage 16 into the exterior container as indicated by arrows e and e'. Thus, the condition of insulation between the stationary arc contact 5 and the movable arc contact 6 is maintained, and interruption of the arcing current of low or medium value is completed.
However, in this known arrangement illustrated in FIGS. 1-3, the volume of the gas storage 13 is designed to achieve extinguishing of the arc under high arcing current values. However, when low or medium current values are employed for arcing, the resultant thermal energy of the arc 20 is such that the pressure rise in chamber 13 is insufficient to achieve interruption of the arc current and to extinguish the arc. In this known arrangement, in order to ensure forced arc extinction, it is necessary to provide suction in chamber 14 which communicates with chamber 13 through opening 15. This makes it possible to create a situation whereby, even with a relatively low level of pressure increase in chamber 13, there is generated a pressure difference between suction chamber 14 and gas storage chamber 13 and the exterior fluid container. This requires an operating force which is the product of the pressure difference and the sectional area of the cylinder defining the suction chamber. For example, in order to generate a pressure difference of two atmospheres in the case of a cylinder having a diameter of 140 mm, an operating force of ##EQU1## becomes necessary. Since the suction chamber 14 and opening 15 come into communication, the temperature rises due to the thermal energy of arc 20 and the inflow of fluid blown from gas storage chamber 13 against arc 20, and the arc extinguishing fluid containing an electrically conductive gas are drawn into suction chamber 14. As a result, the temperature and pressure in suction chamber 14 rise, and the insulating condition is lowered.